Bioresource Technology 79 (2001) 207±225
The production of poly-(c-glutamic acid) from
microorganisms and its various applications
Ing-Lung Shih *, Yi-Tsong Van
Department of Environmental Engineering, Da-Yeh University, 112 Shan-Jiau Road, Da-Tsuen, Chang-Hwa 51505, Taiwan, ROC Accepted 9 April 2001
This review article deals with the chemistry and biosynthesis of poly-(c-glutamic acid) (c-PGA) produced by various strains of Bacillus. Potential applications of c-PGA as thickener, cryoprotectant, humectant, drug carrier, biological adhesive, ¯occulant, or heavy metal absorbent, etc. with biodegradability in the ®elds of food, cosmetics, medicine and water treatments are also reviewed. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Poly-c-glutamic acid; c-PGA; Biosynthesis; Industrial applications
Poly-c-glutamic acid (c-PGA) is an unusual anionic,
naturally occurring homo-polyamide that is made of D and L -glutamic acid units connected by amide linkages between a-amino and c-carboxylic acid groups (Fig. 1).
It was ®rst discovered by Ivnovics and co-workers
(Ivnovics and Bruckner, 1937; Ivnovics and Erds,
1937) as a capsule of Bacillus anthracis which was released into the medium upon autoclaving or upon aging and autolysis of the cells. It is also well known that the
mucilage of ``natto'' (fermented soybeans, a traditional
food in Japan) is a mixture of polyglutamic acid
and fructan produced by Bacillus natto Sawamura
(Sawamura, 1913; Fujii, 1963). Since Bovarnick (1942)
showed that c-PGA was freely secreted into the growth
medium of Bacillus subtilis as a product of fermentation, several Bacillus species have been shown to produce c-PGA outside the cells. (Cheng et al., 1989; Goto and Kunioka, 1992; Hara et al., 1982a,b; Housewright,
1962; Kubota et al., 1993a,b; Murao, 1969; Thorne
et al., 1954; Troy, 1973). In addition, c-linked glutamic
acid polymers have also been identi®ed in Natronococcus occultus (Niemetz et al., 1997), and in the nematode Hydra (Weber, 1990), it is also found attached to
Corresponding author. Tel.: +886-4-852-3870; fax: +886-4-8523870. E-mail address: firstname.lastname@example.org (I.-L. Shih).
folic acid (McGuire and Coward, 1984) and as an appendage to the structural protein tubulin (Edde et al., 1990).
c-PGA is water soluble, biodegradable, edible and
non-toxic toward humans and the environment. Therefore, potential applications of c-PGA and its derivatives have been of interest in the past few years in a broad
range of industrial ®elds such as food, cosmetics, medicine and water treatment. c-PGA and its derivatives oer a wide range of unique applications including being
used as thickener, humectant, bitterness relieving agent,
cryoprotectant, sustained release materials, drug carrier,
curable biological adhesive, biodegradable ®bers, highly
water absorbable hydrogels, biopolymer ¯occulants,
heavy metal absorber and animal feed additives. These
applications are summarized in Table 1.
Thorough reviews on the biosynthesis and applications of c-PGA produced by microorganisms are scant, although a few mini reviews dealing with this metabolite have been published (Housewright, 1962; Nitccki and Goodman, 1971; Troy, 1982; Kunioka, 1997).
Since there is a revival in interest in using c-PGA and
its derivatives as biomaterials, much research has been
done that has led to a huge number of publications.
The present review will be devoted to a survey of the
main achievements in the biosynthesis of c-PGA by
various microorganisms. Furthermore, the applications
of c-PGA in various ®elds will also be extensively reviewed, on which much attention has been recently focused.
0960-8524/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 8 5 2 4 ( 0 1 ) 0 0 0 7 4 - 8
I.-L. Shih, Y.-T. Van / Bioresource Technology 79 (2001) 207±225
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